The present invention relates to sensing of tissue characteristics in vivo in a patient (human or non-human animal). More specifically, the present invention relates to detection of fluorescence characteristics of tissue for diagnosis and definition (i.e., distinguishing tissues of different types) purposes.
Various medical diagnostic and treatment techniques involve detection of tissue characteristics. For example, checking for fluorescence of tissue has been used for early detection of cancer in the esophagus and other parts of the gastrointestinal tract. Also, such fluorescence has been used to detect plaque in arterial walls. The amplitude, steepness, and spectral location of peaks in the fluorescence (i.e., wavelengths of greatest amount of light) are indicative of the characteristics of the plaque including the thickness of its collagen which supports the fat in the plaque. However, the resolution in such fluorescence techniques has been less than desirable at least in some circumstances where plaque characteristics are important.
Finding the plaque which is most prone to rupture or thrombosis is difficult. That kind of plaque poses the most immediate danger to a patient. Therefore, early detection of certain subtle characteristics of that most dangerous kind of plaque is important. Many plaque detection techniques do not provide sufficient resolution for early detection of the dangerous plaque.
Among various other tissue detection techniques, use of magnetic resonance imaging (MRI) may allow the detection of plaque in arteries.
Another technique used for tissue characteristic sensing is ultrasound. This is useful in some circumstances, but lacks sufficient resolution for other circumstances such as reliable early detection of dangerous plaque.
Infrared (IR) detection of tissue provides information about the tissue characteristics. However, this technique again lacks sufficient resolution for other circumstances such as reliable early detection of dangerous plaque.
Angioscopic imaging of tissue can provide information about condition of arterial tissues. However, this technique involves colorimetry and software that infers the characteristics of plaque indirectly. The indirect inference makes this of questionable accuracy under at least some circumstances.
U.S. Pat. No. 5,061,265, co-invented by the present inventor, issued Oct. 29, 1991, and hereby incorporated by reference, disclosed laser ablation of cardiovascular tissue, such as plaque on arterial walls, by use of a double hood catheter. That technique used a power laser beam exiting an inner hood, passing through a clear fluid between the inner hood and an outer hood, and passing out of an opening in the outer hood. The clear fluid passed out the opening and it, together with the structure of the catheter, prevented build up of burned blood cells or other materials on the inner hood. In that fashion, a high power laser beam was able to apply sufficient power to ablate plaque.
U.S. Pat. No. 4,860,743, entitled xe2x80x9cLASER METHOD AND APPARATUS FOR THE RECANALIZATION OF VESSELS AND TREATMENT OF OTHER CORONARY CONDITIONSxe2x80x9d issued Aug. 29, 1989 in the name of Dr. George S. Abela, the present inventor, is also incorporated by reference. That patent disclosed some underlying techniques of laser ablation, which techniques were modified and improved in the above referenced ""265 patent.
Accordingly, it is a primary object of the present invention to provide a new and improved imaging system and method.
A more specific object of the present invention is to provide improved fluorescence detection of tissues.
A further object of the present invention is to provide improved resolution in detection of characteristics of cardiovascular tissue such as plaque on arterial walls.
Yet another object of the present invention is to provide a catheter technique where fluorescence detection is improved by providing a clear fluid for the light to pass through.
The above and other features of the present invention which will be more readily understood when the following detailed description is considered in conjunction with the accompanying drawings are realized by a system for medical diagnosis including: a catheter with a proximal end and a distal end and having: an outer hood having a first opening disposed therein; an optical fiber having a tip within the outer hood, the optical fiber operable to output a diagnostic laser beam with a central axis extending from the tip through the first opening; and a channel connected to the outer hood and extending along the catheter for supplying flushing solution to within the outer hood such that the flushing solution flows out of the first opening. A detection subsystem is operably connected to the proximal end of the catheter and operable to detect fluorescent light from tissue illuminated by the diagnostic laser beam, the fluorescent light having passed from the distal end of the catheter to the proximal end of the catheter along the optical fiber.
The present invention may alternately be described as a method of medical diagnosis, the steps including: inserting a distal end of a catheter into a patient, the catheter also having a proximal end and including an outer hood having a first opening disposed therein; outputting a diagnostic laser beam from within the outer hood to pass through the opening and be applied to tissue of the patient; sensing fluorescent light from the laser stimulation of the tissue; and supplying clear solution to the opening such that the diagnostic laser beam and the fluorescent light have relatively clear paths.